1. Field of the Invention
The present invention relates to a liquid ejection head and a production process thereof.
2. Description of the Related Art
A variety of systems is proposed regarding a liquid ejection head which ejects a minute droplet at a desired position to form an image. A general liquid ejection head has a construction including an energy-generating element for generating energy for ejecting a liquid, a substrate having a circuit for driving the energy-generating element, an ejection orifice from which the liquid is ejected and a liquid flow path communicating with the ejection orifice. As an example of a process for producing the liquid ejection head having such a construction, there is mentioned a process in which a flow path forming member is directly formed by means of a photolithographic method on a substrate obtained by forming a circuit and an energy-generating element on a silicon wafer. In the flow path forming member of the liquid ejection head produced by such a process, there are limitations on material and thickness from the viewpoint of production. In addition, the flow path forming member is thinly formed from the viewpoint of achieving desired ejection characteristics, and the thickness thereof is generally from several microns to several tens microns. Therefore, the resistance of the flow path forming member to physical shock and vibration may be insufficient in some cases. Further, it may be difficult in some cases to thinly and evenly form the flow path forming member by means of the photolithographic method. For example, a pinhole or gap is formed in the flow path forming member, and so a liquid may leak from a liquid flow path in some cases.
In order to improve the long-term reliability of the liquid ejection head, various investigations have been made from a structural point of view. For example, U.S. Pat. No. 7,600,856 discloses a process in which another member is arranged at a position where no liquid flow path is formed, and a flow path forming member is formed thereon for enhancing the strength of the flow path forming member thinly formed from the viewpoint of a production process. According to this process, another member is filled into the flow path forming member except for a portion where the liquid flow path is formed, and the strength of the flow path forming member can be improved.
In the process described in U.S. Pat. No. 7,600,856, a gap is easily formed at a portion in particular where a side wall of the flow path forming member comes into contact with a substrate as illustrated in FIG. 6 (portion A in particular), and there is a possibility that a liquid may leak from a liquid flow path. That is, in U.S. Pat. No. 7,600,856, the flow path forming member is formed by means of a chemical vapor deposition (CVD) method so as to cover a mold material of the liquid flow path. However, it is however hard for the film-forming gas to reach a part where the mold material provided with a structurally narrow space comes into contact with the substrate. Therefore, the film forming rate at that part becomes low. As a result, a gap such as pinholes or cracks is easily formed in the flow path forming member at a part where the flow path forming member comes into contact with the substrate.
Even when a flow path forming member is formed of a resin, the flow path forming member may be detached from the substrate, or cracking may occur in the flow path forming member at a part coming into contact with the substrate in some cases. When the detachment or cracking occurs, a problem that a liquid leaks from a liquid flow path is caused.
Accordingly, it is an object of the present invention to provide a liquid ejection head capable of reducing liquid leakage from a liquid flow path.